Parameters in mysql_query and mysql_execute

[staticlibs]

This PR adds new optional params argument to mysql_query and mysql_execute functions that allows to pass query parameters to an underlying MySQL prepared statement (that was added in #156).

Parameters are specified as a STRUCT, that can be created inline using row() function:

SELECT * from mysql_query('s', 'SELECT CONCAT(?, ?) a', params=row('foo', 'bar'))
----
foobar

When the whole DuckDB SQL statement, that contains mysql_query() function, is used with PREPARE + EXECUTE (for example, from Python or Java client), then the external client-provided parameters will be forwarded to MySQL:

PREPARE p1 as SELECT * from mysql_query('s', 'SELECT CONCAT(?, ?) a', params=row(?, ?))

EXECUTE p1('foo', 'bar')
----
foobar

EXECUTE p1('baz', 'boo')
----
bazboo

DEALLOCATE p1

In current implementation the statement is re-prepared (re-sent to MySQL server) every time when EXECUTE is called.

The following parameter types are supported: integers, FLOAT, DOUBLE, DATE, TIME, TIMESTAMP, TIMESTAMP_TZ, VARCHAR.

DECIMAL parameters are currently not supported, they can only be specified as strings on API level, so casts to/from VARCHAR can be used instead.

Only positional parameters are supported - STRUCT field names are ignored.

Testing: new tests added for mysql_query and mysql_execute fuctions.

[Mytherin]

Thanks!